SSINS No.: 6835
IN 83-23
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
April 25, 1983
Information Notice No. 83-23: INOPERABLE CONTAINMENT ATMOSPHERE SENSING
SYSTEMS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or
construction permit (CP).
Purpose:
This information notice is being issued to remind all licensees of the
importance of assuring that procedures are both properly developed and
carefully followed. The instances cited relate to the containment system, an
important element in the "defense-in-depth" approach to nuclear safety and
are of particular concern because some had apparently existed for several
months without detection.
Description of Circumstances:
Seven instances have been compiled since April 1981 that indicate
insufficient licensee management attention is being given to maintaining
containment integrity, and to the operability of equipment related to the
containment function.
At LaCrosse Nuclear Generating Station on two separate occasions in April
1981, a containment high-pressure sensing switch was temporarily isolated
while the plant was at power, thus defeating automatic emergency core
cooling system actuation. A proposed design change was being implemented
without proper review and authorization. Subsequently, it was determined
that under 10 CFR 50.59, the change should not have been made without
concurrence by the Nuclear Regulatory Commission.
At Oconee Nuclear Station, in March 1982, an NRC inspector found that a pipe
cap had not been reinstalled on a test connection to a containment pressure
sensing line, as required by the relevant test/calibration procedure last
performed in July 1981. As a result, containment integrity had been violated
for that interval, and the sensing system (although operable) was degraded.
Containment pressure as sensed by the system could be significantly lower
than actual containment pressure.
At Dresden Unit 2, there is a local sight (gage) glass on the side of the
suppression pool to show the level of the water in the pool. In October
1982, the
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licensee reported finding the upper isolation valve and the vent valve open.
This violated containment integrity, and allowed free communication between
the inerted atmosphere of the suppression pool and the outside atmosphere.
In fact, both the upper and lower isolation valves should be closed, except
when calibrating other level-sensing devices, while shut down.
At Kewaunee Nuclear Station, the licensee reported in October 1982 that all
containment pressure-sensing lines were found to have pipe caps installed,
thereby defeating the entire containment pressure-sensing systems, including
alarm and emergency core cooling functions. The licensee believes the caps
were improperly left in place after required testing and calibration about
five months earlier.
At Arkansas Nuclear One on December 16, 1982, during performance of routine
refueling surveillance of the reactor building pressure transmitters, the
licensee discovered that the inlet ports on two transmitters were blocked
with brass pipe plugs. One of the two inoperable transmitters provide an
input to a recorder; however, the other instrument provides a signal to one
of three engineered safeguards actuation system (ESFAS) safety channels.
With this transmitter input plugged, the ESFAS logic for reactor building
high pressure was reduced from a 2 out of 3 to a 2 out of 2 trip logic
required for the initiation of engineered safeguards. It was determined that
the plugs were installed on February 20, 1981, as a prerequisite for a
containment integrated leak rate test and remained installed until their
discovery on December 16, 1982 during the next refueling outage. The
licensee attributed the specific cause to use of an inadequate temporary
test procedure change which allowed plugs to be installed in the pressure
transmitters but did not contain a step specifically requiring their
removal.
At Calvert Cliffs Nuclear Power Plant on June 18, 1982, an NRC inspector and
licensee representative were examining containment system boundaries of Unit
1 in preparation for a containment integrated leak rate test. They
discovered two of the four safety-related containment pressure sensing lines
were isolated with pipe caps inside containment, thus deactivating
containment pressure monitoring instruments which provide protection signals
to the safety systems. A review of records and logs from the previous
operating cycle revealed that this inoperable condition did not exist prior
to the last refueling outage. The licensee reviewed records and conducted an
investigation but was unable to determine who installed the pipe caps; when
they were installed; or with what authorization. It was however assumed that
they were installed by mistake during the prior outage.
In each of the above instances, in normal operation there is little
difference between containment pressure and ambient atmospheric pressure.
For pressure differences of the magnitude expected in normal containment
system operations, verification techniques such as trend plotting of
averaged output values may be beneficial to supplement visual verification
of individual component status.
At Salem Nuclear Station, on October 17-18, 1982, the licensee found during
containment purge operations that radiation monitor sensing lines, which
provided high radiation level automatic containment isolation signals, had
been temporarily capped while making a design change, and the caps had not
subsequently been
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IN 83-23
April 25, 1983
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removed as required. The work had been performed during a refueling outage
which terminated on April 11, 1982.
Systems for sensing airborne radioactivity typically include a blower or air
pump to extract a sample of the air being monitored and direct it through or
past sensors. For the very low levels of activity normally expected, some
technique is required for integrating total activity over a known time
interval. To achieve acceptable accuracy of calibration, the actual flow
(quantity of air in the total sample) must be known. Periodic observation of
the flow measuring device provides a simple means of verifying this aspect
of system operability, and would have detected the capped lines at Salem.
Although all the examples cited above involve sensing of containment
atmosphere conditions, (pressure and radioactivity) and the licensee event
reports do not in each case identify why the anomalous condition existed
undetected for so long a time, the NRC staff is of the opinion that
inadequate surveillance procedures, or inadequate implementation of the
procedures, or both, were the underlying cause(s) of the situations.
Further, a variety of other instances have appeared in licensee reports
indicating that surveillance of operability of other safety-related systems
could be improved.
No specific actions are required of any licensee by this Information Notice.
If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: J. B. Henderson
(301) 492-9654
Attachment:
List of Recently Issued IE Information Notices
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